FANTASTIC post Simon, and great comments Steve2 as well...(and everyone in fact)
Another thing to add is that : Nothing is constant. Things change (evolve) over time, so what was PERCEIVED to be truth once, needs re-evaluating as more information comes to light. Most religions don't do that....
For instance, Christians (and witnesses in this case) will take the accounts in the OT as factual and acceptable behaviour. (eg Lot committing incest with his daughters, or the killing of babies by soldiers etc) But we know now that there is NEVER an acceptable reason for such behaviour!
I challenge a witness to try and tell us otherwise!